Light projection



Jan. 30, 1923. 1,443,731

D. F, COMSTOCK. LlGHT PROJECTION. FILED FEB. 9. 1920. 5 sHEETssl-EE-T l iff-5U@ m26@ g1 jams@ ff/owasa ci@ Jan. 30, 1923. 1,443,731

D, F CGMSTCCK.

LIGHT PROJECTION, FILED Fam. 9, 1G20.

5 SHEETS-SHEET 2 Jan. 30, 1923.

5 SHEETssHEET 3 D, F. COMSTOCK. LIGHT PROJECTION. FILED FEB. 9, 1920.

WMANMYN PV Jan. 30, 1923.

D. F. COMSTOCK.

L| @HT PROJECT l oN 5 SHEETS-SHEET 4 Fl LED FEB 9. 1920 s. k C NWJ m 0 ,TUM a @Y n e /0 v 6 z Lm .z n Z .W .6 f e j n a jf Jan. 30, 1923. 1,443,73l

DA F. COMSTOCK.

LIGHT PROJECTIONV FILED FEB. 94 1920. 5 SHEETS-SHEET 5 if@ ,mi

Patented Jan. 30, 1923.

UNITED STATES Lani COMSTOCK 8c WESCOTT, INC.,

MASSACHUSETTS.

OF BOSTON, MASSACHUSETTS, A CORPORATION OF LIGHT PROJECTION.

Application led February 9, 1920. Serial No. 357,267.

To-all urk-m t may concern.'

Be it known that I, DANIEL F. CoMsToCK, a citizen of the United States of America, and resident of Cambridge, inthe county of Middlesex and State'of Massachusettshave invented new and useful Improvements in Light Projections, of which the following is a specification.

This invention relates to an apparatus 'for eliminating the glaring rays from a beam of light by refiecting, deflecting, absorbing, diffusing or otherwise intercepting those rays of a beam of light having certain directional cliaracteristics, this application being a companion to my copending application Serial No. 92,750, filed April 21, 1916.

Broadly considered the invent-ion consists in an application and utilization of the princip'le of the Critical angle of reflection whereby rays of different directional characteristics may be separa-ted and thereafter treated independently and in any way desired, as for example distributing or projecting a certain part of a beam of light in 25 a predetermined zone, the distribution in that zone being of any desired nature, while treating the other part of the light which if projectedrwould fall outside that zone likewise independently and in any desired` manner. For instance, this latter light may be either eliminated altogether or projected in some manner other than the light falling within the predetermined zone above mentioned.

, The object of the invention is to provide a translucent screen for headlights having internally thereof a series of prisms whose oblique Vsurfaces act as critical angle reflectors to reflect all light rays directed above the predetermined boundary. It is `a further object to provide means .for diffus# ing, absorbing, deflecting, reflecting or otherwise intercepting the reflected light.

An additional object in connection with the use of my invention in automobile headlights is to provide a translucent screen whereby a relatively large area close to the screen is illuminated with. a light of a certain intensity and a. more restricted area at a greater distance in front ot' the screen is illuminated by a light of approximately. the

same intensity at the area illuminated. I

I have illustrated several referred em- -bodiments ofmy invention 1n the accompanying drawings in which- I Figure 1 is a front view of my improved translucent screen;

Figure 2 is a cross section of Fig. 1 on line 2-2;

Figure 3 is a view similar to Fig. l2 but o f a modified form of the device;

Figure 4 is a view similar to F'ig. 2 but of a slightly modified form;

Figure 5 is a broken away view on line 5--5 of Fig. 4;

Figure 6 is a diagram illustrative of the principle of the invention;

Figure 7 isa front-view of a modified form of the device;

Figure 8 is a front view of a further modification of the device; i

Figure 9 isa front view of another modification of the device;

Figure 10 is a front view of still another modified form of the device;

Figure 11 is a front view of a differently modified form of the device;

Figure 12 is a cross section of taken on line 12-12;

Figure. 13 is a cross section of Fig. 11 taken on line 13-13;

Figure 14 is a cross section taken on line- 111-14;

Figure 15 is a. vertical cross section of' a modified form of the device;

Figure 16 is a vertical crosssection of a further modification of the device; l

Figure 17 is a front view of a compound form of the invention;

Figure 18 is a vertical cross section of Fig. 17; A

Figure 19 is a horizontal cross section of i Fig. 17

Figure 20 is a horizontal cross section of a modifiedform of the device;

Figure 21 is a cross section of Fig. 20 on the line 21-21;

Figure 22 is a cross section of Fig. 20 on the line 22-22;

Figure 23is a view showing in a general way the distribution of the light projected on a surface placed in front of the headlight Fig. 11

bf Fig. 11

by theform of screen shown in Figs. 1 to 4, viewed from the headlight side of the surface' F igure 24 is a View similar to Fig. 23 but showing in a general way the light distributed by the form of screen show n in Fig. 7;

Figure 25 isa View similar to Fig. .23' but showing thelight distributed by the form of screen shown in Fig. 8;

Figure 26is a View similar to Fig. 23 but showing the light distributed by the form of screen shown in Fig. 9;

Figure 27 is a View similar to Fig. 23 but showing the light distributed by the form of screen shown in Fig. 10,;

Figure 28 is a View similar to Fig. 23 but showing the light distributed by the form of screen shown in Figs. 11-14;

Figure 29 is a View similar to Fig. 23 but showing the light distributed by the form of screen shown in Fig. 15, the figures being partly'brokenf away at top and bottom; and

Figure 30 shows my 1 improved screen mounted in a headlight.

The method in which the simplest form of my device functions is indicated by the diagram shown in Fig. 6. In this figure, the reflecting prism is designated A, having the oblique reflecting surface a, the line :zr-:1; being the normal to the reflectingA surface. Opposite to the reflecting prism. in the reverse position is the counter refracting prism B with its oblique surface b opposing the surface a.

The arrow line 0-0 represents a ray of light entering the prism A. so that it strikes the surface a at the critical angle and is reflected to c while the line ZL-d" represents a ray having a smaller angle of incidence, which is therefore not reected (eX cept in part as hereinafter pointed out) but passes through to rf. The upward refraction which occurs as the ray leaves thev surface-a is counteracted by the downward refraction as the ray enters the parallel surface b andthe ray is in effect a straight ray.

As shown by this diagram the angle hl, which is the angle the. reiiecting surface makes with the vertical, ispreferably made Such that it reflect-s all rays which strike the -lens at a. small predetermined angle above the horizontal along the line 0-0 or at any greater angle above the horizontal. All rays transmitted through the prisms emerge in the same direction in which they enter.

The angle N will depend upon the refractive index of the media, and upon the angle above the horizontal through which it is desired to permit the rays to pass. I have found that a prism of ordinary glass having a refractive index of 1.5 and a critical angle oi' 4h70 is suitable.

The upper surface of the redecting prism upon which the reflected ray c impinges maybe treated so as to absorb, to diffuse, to deflect, to reflect or to otherwise obstruct the light which reaches it, or as an alternative various parts of such surface may be `treated in different ways. If thesurface is porting means of the headlight o r other device in lwhich it is to be used. The plate 31 carries the horizontally disposed prisms 34 whlch interfit` with the oppositely faced prisms 35 carried by the plate 32. It is to' be noted that both outer faces of the assembled lens are plane. I

In the form shown in Fig. 3, the screen comprises two similar outer sheets of plane glassl 36 which hold therebetween, a plurality of separate prisms arranged in two opposed series 37 and 37. The screen assembly is clamped in a rim or holder 38. It

lwill be observed that although this screen is quite different in construction from that-of Figs. 1 and 3, the resultant lightwill be identical.

In Fig. 4 is shown a screen si-inilar to that of Fig. 2 except that insteady of being held together by a rim or holder, the edges of effect upon 'the the two glass members are cemented or fused together as indicated at 39.

Fig. of Fig. 4 and there is indicated at 40 that the upper surfaces of the reflecting prisms may be frosted, roughened, painted, silvered or otherwise prepared to absorb, diHuse or reflectv the light which reaches them. In

Fig 30 I have shown my improved, screen mounted ina usual type of headlight. The headlight comprises the shell 60, the parabolic reflector 61, incandescent bulb 62 and the rim 63 which holds the screen in place. rllhe screen shown is that illustrated in Figs. 1 and 2 having the members 31 and 32 retained in the frame 33.

In F ig. 23 I have jshown the resultant light effect upon a screen of a beam of light after passing through the lenses shown in Figs. 1 to 4. The Figures 23 to 29 indicate in a. general way the light distribution afforded by the several forms of screen. rIhese figures represent approximately the effect produced by the light thrown upon a surface placed in front of the light and as viewed from the side of the surface adjacent the light source. These figures do .not show 5 is a cross section on the line 5-5 darker portion representing the small inl tense cones and the marginal part the larger Cone of transmitted light. It will be understood that the upper edge of the lightv may be made higher or lower relative to the light by a variation in the angle of the reflecting surface, designated N in the diagram shown in Fi 6, in constructing the screen'.

In igs. 7 to 22 I have shown various differentv conformations of the reflecting and counter refracting prisms to accomplish different distributionsV of the light. It is to be understood that these various forms may be made by any one of the several structural methods illustrated in Figs. 2, 3 and 4. In Fig. 7 the prisms .curve up on one side of the screen at a and curve down on the other at b -which would give a light distribution somewhat as shown in Fig. 24. The upward curvature' at a causes the portion d of the light distribution, the angle oi' the upper edge of this portion depending upon the angle of the tangent to the upwardly curved portion a of the prisms. The central portion ofthe lens with its horizontal prisms c retains the major portion-A of the light below the horizontal line c and hence the portion-a does not receive as much light as the'adjacent portion below the' line c. Thedownward' curvature at #causes a part of the lightto be deiected from the portion b', the angle ofthe \lower edge of this portion depending upon the angle of the tangent to the downwardly curved portion of the prisms. In Fig. 8 the prisms also curve up on'one. side of the screen at a and the remainder c of each prism is hori.- zontal which gives thev light distribution shown in Fig. 25. This distribution differs fromthat shown in Fig. 24 in that the curved top'I is somewhat higher in the center. These two forms may be desirable for use in automobile-headlights with the two headlights of the machine having reversed lenses so that the sides'of the road would be i lluminated to'a greater height than the road directly in front ofthe machine.

In Fig. 9 I vhave shown theprisms placed on a curve d concave upward which will distribute the light as shown in Fig. 26. Here the light has an upper boundary which is a crescent-shaped plane the depth of the cresent depending upon the angularity between the tangents to the curve of 'the prisms.

In Fig. '10 I haveshown `a form of lens which. comprises three sets of prisms, the center setff beinghorizontal, and the side sets e and g being similar and slant'ing out-l wa'rdly and' downwardly. This arrangement of prisms will give a light distribu-y tion las shown in Fig. 27.. The resultanty lbeam mayl bel considered as three separate partly cri-extensive beams. The centra-l beam passing through the horizontal prisms has an upper boundary deiined by a horizontal plane as shown at f. beam g has a slanting upperboundary denedby the plane g', the angle of the prisms -g corresponding to the angle of the boundg and similarly the lateralbeam e is defined by the plane e. These combined form 'a beam whose illuminativeefect is as F ig. 14 is taken at an angle on, the liney 14-14. 'Such a construction gives a light distribution as shown in Fig. 28. Here are the equivalent of two partly coextensive beams, that passing through the portions cof the prisms being vbounded by the.l line 7c and that through the portions m being bounded by -the lime m. The resultant beam therefore has'a boundary formed by a V-shaped plane.

In Figs. 15 andV 1-6 are shown two forms of screen in which `the reilecting surfaces 41` and 42 are respectively convex and concave. In either of these cases the angle which marks the point on one side of which light is reflectedv and in the other side of which, it is transmitted, varies throughout the curve. Therefore in both cases the cut oil' of the upwardly inclined rays is gradual and, instead of a definite limit to the light diffusion, the light will appear in the general form shown in Fig. 29.

In Figs. 17 to 19 I have shown a screen composed of three plates'of glass and having two separate sets of prismsv at right angles to each other. The plate 44vcarries the horizontal extending reflecting .prisms 45 which 'reiect rays more than a predetermined angle above the horizontal. These extending reflecting prisms 48 which serveto refiect light striking them inclined more than a predetermined amount to the left as seen'in Figs. 17 and 19. The prisms intert with the vcounter refracting prisms 49 on the plate 50. The resultant beam of the light from this screen will be ilattened not only on the top but one side, in this case the left, and a cross section of -tlie beam would have the approximate shape of the quadrant sector of a circle.-

In Fig. 20 I have shown a horizontal crosssection of a screen in which the reflecting surfaces are warped, being at 'a greater angle from the horizontal at the right and, as

The lateral shown in 'F ig. 22, than at the left end, as shown in Fig. 2l. In this case the resultant light beam will have an inclined upper surface instead of the flat surface shown in Fig. 23.'

lVliile I have described my new form of screen in connection with an automobile headlight it is obvious that it is much wider in its application. It will be of utility in connection with various schemes of floodlighting of buildings, advertisements, etc.

In such uses its function would be to serve to deliver a stream of light limited in one or more directions. In varying uses the screen might be rotated grees to limit the light so as not to pass be- `vond the side ofa building or sign orrotated one hundred and eighty degrees so as not to pass below a given line.

I have, by way of example, shown a num- J ber of various forms of my device both in regard to structural details and in regard to the prismatic lforms and their relation to the resultant light beam. It is to be understood that these examples are merely illustrative of the broad and varied application of my invention.

A secondary characteristic of criticalanglereflectors which -has been ignored herein for `the sake of clearness and brevity is the following. lVhile most of the rays striking the critical-angle reflecting surface at angles less than the critical angle, i. e., at angles more abrupt than the critical angle, are transmitted, a certain proportion of such rays are reflected, the proportion being larger immediately within the critical angle but rapidly decreasing to a minimum of about four per cent at the perpendicular. lVith the screens herein disclosed. this reflected portion of the rays incident Within the critical angle is treated in the same manner as the reflected rays incident at angles greater than the critical angle.

I claim: l v

l. A translucent screen having total-ie through ninety de- .and means'- for diffusing and transmitting the reflected rays.

3. A translucent screen for `headlights comprising prismatic elements'having totalrelecting surfaces for reflecting rays incident thereto atertain angles and having diffusing means at other surfaces to diffuse the reflected light. l

4. A translucent screen for headlights comprising interlitting prismatic elements, certain surfaces of the elementsY being obliquely disposed in the" path of the light to reflect the class of rays inclined in one direction relative to the horizontal while transl mitting the class of rays inclined inthe other direction relative to the horizontal, and diffusing means between certain surfaces of the interfitting prismatie elements to diffuse one class of rays.

5. A translucent screen for headlights comprising prismatic elements having totalreflecting surfaces disposedobliquely in the path of the light to reflect rays inclined in one directionl from the horizontal, and means for diffusing upwardly inclined rays.

6. A translucent screen for headlights comprising prismatic elements having totalreflecting surfaces disposed obliquely in the path of the light to reflect upwardly inclined rays while transmitting other. rays, and having diffusing mea-ns above said surfaces in the paths lof the reflected rays to diffuse same. v

Signed by me at Boston, Massachusetts, this 31st day of January 1920.

DANIEL F. COMSTOCK. 

